Three-dimensional (3D) imaging typically involves sweeping or scanning a beam across a volume and measuring the radiation reflected or scattered by an object in the volume. The angle or position of the beam corresponds to the object's transverse (x and y) coordinates, and the delay between the emission of the beam and the arrival of the reflected or scattered radiation, or time-of-flight, indicates the object's range, or location in z. The returned radiation is typically sensed with a detector array, such as an array of avalanche photodiodes, and used to create a 3D image of the scene being illuminated. In general, the range of the system depends on the sensitivity of the detector array, with better sensitivity giving better range performance for a given transmitter power and aperture size.
The range resolution is often limited by the precision of the time-of-flight measurement, which depends on the timing jitter of the transducer that detects the scattered or returned radiation. For example, the timing jitter of the avalanche photodiodes used in current near-infrared imaging laser radars is about δt=350 ps, limiting the range precision to about 5.3 cm. While range granularity of a few centimeters is good enough for imaging many objects, higher resolution and improved capabilities, such as face recognition, are often desired. Unfortunately, sensitive detectors with lower timing jitter cannot be easily arranged into arrays.
Thus, a need exists for a 3D imaging system that operates with low timing jitter and good sensitivity.